OBSERVATORY

By Henry Fountain

Published: November 9, 2004

Ancient Beauty Secrets

Mary Kay wasn't passing out Cadillacs back then, and Avon wasn't calling, but cosmetics were in vogue even in ancient Roman times. Contemporary accounts describe the use of rouge and other types of makeup, and it is known that a fair complexion was preferred.

Chemists at the University of Bristol in England have now revealed one way women achieved their pale looks. Analyzing the contents of a small tin of white cream that was unearthed last year at an archaeological dig in London, the scientists conclude that it was a cosmetic face cream.

The tin, about two and a half inches in diameter by two inches high, was found at a temple complex dating to the middle of the second century A.D. When opened, the tin was found to have cream still in it, complete with the finger marks of the last person to take a dab.

Analysis of the cream, reported in the journal Nature, showed that it contained about 40 percent animal fat (probably from sheep or cattle) and 40 percent starch by weight. A tin compound, stannic oxide, was the other major ingredient, and there was no evidence of any perfume.

The researchers suggest that the fat was heated, possibly to bleach it, and that the stannic oxide (easily made by heating tin) served only as a white pigment. There is no known literature indicating the Romans thought it had any medicinal value.

To test the cream's effectiveness as a cosmetic, the researchers cooked up their own batch using the same ingredients. They found that when rubbed on the skin, it initially felt greasy as body heat melted the fat. But that was quickly replaced by a smooth powdery texture because of the starch. And the stannic oxide left the skin with an overall opaque whiteness. So, the researchers say, the cream may have served as a foundation layer.

Most Roman face paint, the researchers point out, was made with lead, which is toxic. Since Romans often confused tin with lead, the makers of this cream may have thought they were using lead as well. By using tin, though, they ended up with a product that was much safer.

Bugs Stay High and Dry

Gerris remigis is a remarkable insect: it walks on water. The bug, known as the common water strider, has long legs that repel water, creating dimples whose surface tension keeps the bug afloat.

There is nothing mystical about it, but there has been some mystery. Scientists had thought that what made the legs so hydrophobic was a waxy secretion on the surface. But now two Chinese researchers report in Nature that, by itself, the wax isn't enough to keep the bugs high and dry. Instead, they say, the striders have tiny hairs on their legs with even tinier grooves that trap air.

To test whether a waxy surface was enough to keep the bug afloat, the researchers created an artificial leg from a quartz fiber that was coated with an extremely water repellent compound. They found that the surface tension was enough to support the bug at rest, but not when it was moving around.

Electron micrographs showed that the water strider's legs have tiny needlelike hairs, less than 3 microns, or 0.0001 of an inch, in diameter at their widest point and about 50 microns long. Each of these hairs, in turn, has tiny grooves, on the order of nanometers. Air trapped among the hairs and grooves contributes to the legs' hydrophobic quality, increasing its ability to float.

The researchers found that the supporting force of water is enough to allow the bugs to survive even in a storm, when they bounce around to avoid being drowned by raindrops.

Joining Forces on Quakes

Earthquake engineering will take a grand leap forward next week with the official opening of a collaborative network of laboratories around the United States. The 10-year project, the Network for Earthquake Engineering Simulation, links 15 university labs with large-scale experimental equipment like shake tables, tsunami wave basins and centrifuges to help engineers study what happens to buildings, bridges and other structures and soil during quakes.

The labs will be linked through Internet 2, the high-speed networking project developed by a consortium of more than 200 universities. The connections will enable them to share data and simulation software. Researchers at different labs will be able to collaborate in real time.

The Science of Spin

The finches that Charles Darwin described in the Gal?gos Islands are a classic example of divergent evolution. The beaks of different species evolved in response to specific evolutionary forces -- different foods available on the various islands.

But nature is also full of examples of related but geographically isolated species that have similar physical or behavioral traits. The question in such cases is whether these shared traits evolved separately -- what is called convergent evolution -- or once in a common ancestor and were passed down to the modern species.

Dr. Todd A. Blackledge has supplied an answer in the case of a complex behavioral trait, web spinning by spiders. In a study of nine related species on three Hawaiian islands, Dr. Blackledge and a colleague, Rosemary G. Gillespie, found that separated species evolved similar web styles independently.

Dr. Blackledge, who conducted the study while at the University of California at Berkeley but is now a postdoctoral researcher at the University of California at Riverside, said he had not expected to find such convergent evolution. ''I was originally interested in how web-making behavior had diversified,'' he said. But as he looked at webs, he found some that were remarkably similar to those made by other species on other islands.

In the study, published in The Proceedings of the National Academy of Sciences, Dr. Blackledge used a system to objectively measure what he had observed anecdotally. He gauged similarities between webs based on factors like the number of spokes and the density of the silk strands woven among them. He found three instances where two species on different islands made webs with similar architectures.

Then, using genetic analysis, he and Dr. Gillespie traced the spiders' lineage to find out how closely related the two species in each pair were. The answer, in at least two of the cases, was that the species were only distantly linked, supporting the idea that their similar web-spinning behavior evolved independently.

The next task for Dr. Blackledge is to determine what evolutionary forces might have acted on the spiders to result in such similar behavior. One possibility, he said, is that different species on different islands eat the same kinds of insects. ''Certain shapes are better for catching certain types of prey,'' he said. But other factors, like the type of vegetation and the amount of shelter, could play a role. ''All of these different variables probably interact,'' he said, to lead two species to make almost identical webs.